"This strong increase is partly explained by the long weekend shifting to March from April in 2013," Sacci said in a statement.
"New vehicle sales also exhibited a sudden, robust increase in April 2013 sales figures."
The Trade Activity Index (TAI) increased by five points to 61, up from 56 points in March. The seasonally-adjusted TAI improved by 11 index points to 65 in April.
"[This]... indicates that the surge went beyond seasonal factors and the long-term trade survey trend," Sacci said.
Despite the improvement between March and April, trade conditions on average improved by about by 2 index points in the first four months of 2013 compared to the same period last year.
Sacci said sales volumes and new orders, which increased by 10 and 8 index points respectively in April 2013, were mainly responsible for the increase in the TAI.
"Such levels were last registered during the intense trading period at the end of 2006."
Supplier deliveries, inventories, and backlogs on orders improved moderately by 1 to 3 index points between March and April.
"The upward pressure on sales prices remained high, but stable in April 2013 as the index increased by 1 point to 62 after easing by 1 point in March 2013."
Trade prospects (TEI) for the next six months remained positive, with the TEI on 64 points, compared to 63 in March.
The seasonally adjusted TEI increased to 64 points in April, from 62 in March, and averaged 62 in the first four months of 2013.
Expected sales and input price indices both increased in April.
The expectations on input prices for the first four months of 2013 were on average four index points higher than in 2012, while the average expectations on sales prices was two index points higher.
Employment conditions in the trade environment remained positive in April, with the index constant at 52.
The index on six-month employment expectations improved from 53 in March to 54 in April.